Stabilized jet fuel compositions



United States Patent f 3,102,798 STABILHZED JET FUEL CGMPQSITIGNS Harold D. (Brloff, Oak Park, Mich, assignor to Ethyl Corporation, New York, N.Y., a corporation of' Virginia No Drawing. Filed .iuly 10, 1959, Ser. No. 826,116

8 Claims. ((Il. 4- 3-76) This invention relates to jet aircraft fuel compositions they interfere with normal fuel combustion as well as lubricating oil temperature control. The jet fuel thermal stability problem is so serious in some fuels that their use can eventually lead to engine failure of the turbine section due to uneven temperature pattern-s.

Prior investigators have found that conventional gasoline antioxidants are incapable of overcoming this problem. For example, it has been stated that neither 4 methyl-2,6-di-tert-butylphenol nor N,N-di-sec-butyl-pphenylenediamine, both well-known antioxidants, improves the high temperature stability of jet fuels. Indeed, some gasoline antioxidants have been shown to increase the severity of the problem. Consequently, other types of additives have been investigated. One approach has been the use of dispersants in an attempt to keep the deposits suspended in the fuel, and thereby prevent them from adhering to critical engine surfaces. However, this approach has not proved satisfactory because the deterioration of the fuel does occur under jet engine operating conditions and little, if any, improvements in engine performance has been attained. Another approach has been the use of various jet. fuel treating procedures. These are not always satisfactory because they are expensive and complicated, and in some cases, little improvement is achieved.

An object of this invention is to alleviate the thermal stability problems in jet fuels. Another object is to provide new jet fuel compositions which are characterized by a high degree of thermal stability in jet fuels. A still further object is to provide processes of inhibiting deterioration of jet fuel normally tending to occur at elevated temperatures below the cracking temperatures of the fuel during operation of the aircraft. Other objects will be apparent from the following description.

The above and other objects of this invention are accomplished by providing jet fuel containing from about 0.001 to about 0.2 percent by Weight of a 2,2'-thiobis-(4- halo-fi-alkylphenol). The thermal stabilizers of this invention exhibit the unique property of greatly improving the thermal stability of jet fuels and this effectiveness is independent of the hydrocarbon types from which the jet fuel has been prepared. Thus, the present invention affords extreme protection against thermal instability of all present day jet fuels.

The jet additives of this invention overcome the jet fuel thermal instability problem by conferring greatly improved thermal stability characteristics upon the fuels. Thus, a direct benefit accruing from the practice of this invention is the considerable reduction in the amount of insoluble products formed when the jet fuels of this invention are subjected to elevated temperatures. Hence, markedly reproducts which heretofore deposited in the fuel system. The additives of this invention do not introduce secondary problems in use, such as foaming of the fuel at high altitudes, emulsifi cation difficulties, interference with low temtemperatures to the point where deposits are so severe that r duced is the amount of insoluble thermal decomposition 3,102,798 Patented Sept. 3, 1963 perature flow and the like. At the same time, all of these advantages are achieved in a simple manner and at very .low cost. j

It is known that jet fuels tend to deteriorate when subjected to the condition of elevated temperatures below the cracking of the fuel, i.e., temperatures in the range of about .3 00 to about 500 F. Thus, another part of this invention is a process of inhibiting such deterioration which comprises subjecting a jet fuel containing from about 0.001 to about 0.2 percent by weight of a 2,2-thiobis(4 halo-6-alkylphenol) to said condition. Thus, enhanced thermal stability of a jet fuel is achieved by blending with the fuel from about 0.001 to about 0.2 percent by weight of a 2,2'-thiobis-'(4-halo-6-alkylphenol). A pre ferred range of additive concentration is from 0.005 to about 0.05 weight percent of such a 2,2'-thiobis-(4-halo-6- alkylphenol). This concentration range is preferred as it has been found adequate to very effectively stabilize a vast majority of the fuels tested.

wherein R is an alkyl group, preferably branched on the alpha carbon atom, and containing from 3 toabout 12 carbon atoms, and X is a halogen such as chlorine, broinc and iodine.

Preferred additives of this invention are the 2,2-thiobis- .(4-halo-6-alklphenol) compounds in which the alkyl group is tertiary and contains from 4 to 8 carbon atoms. These preferred additives are particularly effective in improving the high temperature stability characteristics of the jet fuels. Among these preferred compoundsthose which have a tertiary butyl group in the 6 position of each benzene ring are especially preferred as outstanding results have been achieved with such compounds.

Another preferred group of compounds within the above definition are those in which the halogen atom, X, is chlorine. These compounds not only impart excellent thermal stability to a jet fuel, but are also readily prepared in high purity and at low cost. The most particularly preferred additive of this invention is 2,2'-t-hiobis-(4-chloro-6-tertbutylphenol) The jet fuels whose thermal stability is greatly improved pursuant to this invention are principally hydrocarbon fuels which are heavier than gasoline, i.e., distilled liquid hydrocarbon fuels having a higher endpoint than gasoline. In general, the jet fuels can be comprised of distillate fuels and naphthas and blends of the above, including blends with lighter hydrocarbon fractions, so long as the endpoint of the final jet fuel is. at least 435 F. and preferably greater than 480 F. It will be understood, however, that the jet fuels which are employed according to this invention can contain certainother ingredients such as alcohols or the like, provided the resulting fuel blend meets the specifications imposed upon jet fuels. Volatile and hydrocarbon composition requirements of a jet fuel are primarily imposed by the nature of jet engine operation. Thus, it is impossible without catastrophic effects to employ an ordinary gasoline as a jet fuel due to the ordinarily high volatility of gasoline.

Until the present, the major use of jet fuels has been scope point at mixture of up to distillate. 'It is a fuel performance and also must have a '90 percent evaporation All of the military jet fuels are encompassed within the of this invention and they include J P-3, J P-4, LIP- and JP-6 The requirements for three of these iiuels, namely JP-3, JP-4- and J P-5, are embodied in Specification MIL-J-5624-D dated December 24, 1957. LIP-6 requirements'iare outlined, in Specification MIL-F-25656 (USAF) dated September 10, 1956. v

In general, JP-3 is referred to as a high vapor pressure type fuel which may be a mixture containing up to about 7 0 percent gasoline and about 30 percent light distillate. One or the requirements set forth in the Military Specification is that LIP-3 must have a 90 percent evaporat on 470 F. and a specific gravity ranging from 50.0 00 60.0 API. 7

JP-4 is a low vapor pressure type fuel which may be a [about 65 percent gasoline and 35 percent especially designed for high altitude minimum temperature at 470 F. However, in distinction to JP-3 the 20 percent evaporation minimum temperature is 290 F. instead of 240 F. as with JP-3. The gravity requirements are from 45.0 to 570 API.

JP-S is a high flashpoint type fuel which is an essentially fractionated kerosene having a percent evaporated minimum temperature of 400 F. and a maximum endpoint of 550 F. It is heavier than the other fuels, the gravity requirements ranging from 36-48 API. 7

JP-6 is also a distillate fuel having a minimum initial boiling point of 250 F. and a 90 percent evaporation point maximum of 500 F. The gravity of this fuel may 'vary from 37.0 to 50 API.

Other requirements of these fuels are as described in the Military Specifications referred to above. Whereas the concentrations of additives of this invention liavelbeen described above in terms of weight percent of the fuel and this terminology is used in the subsequent examples in the specification, it is common practice to express additive concentrations in pounds per 1,000 barrels of fuel treated. Since the gravity of these fuels varies from about 3 6 API to 60 API, this expression is only approximately precise in terms of weight percent. For a 36 APT gravity fuel, 0.001 percent by weight corresponds roughly to 3.0 pounds per 1,000 barrels, whereas for a 60 API gravity fuel 0.001 percent by weight of additive amounts to about 2.6 pounds per 1,000 barrels. Thus, for a JP-3 fuel 0.001 weight percent is from about 2.5 8 to about 2.75 pounds per 1,000 barrels and 0.2 weight percent'is equivalent to 516-550 pounds per 1,000 barrels. In a -JP-4 fuel 0.001 percent by weight amounts to about 2.6-2.8 pounds per 1,000 barrels and 0.2 weight percent is equivalent to 520-560 pounds per 1,000 barrels. For JP-5 \fiuel 0.001 percent by weight amounts to from 2.75- 3.0 pounds per 1,000 barrels and 0.2 Weight percent is equivalent to 550-600 pounds per 1,000 barrels, etc. Even though the gravity of the fuels vary, an excellent approximation to the weight percent can be obtained by converting from pounds per 1,000 barrels.

4, Example 1 To 100,000 parts of fuel A is added with stirring one part (0.001 percent) of 2,2'-thiobis-'(-4-chloro6-tert butylphenol) dissolved in 20 parts of ethanol. The resulting fuel is found to possess improved thermal stability characteristics.

' Example 2 To 100,000 parts of fuel B is added 200 parts (0,2

percent) of 2,2'-thiobis- (4 bromo-6-isopropylphenol) dissolved in 1,000 parts of methanol. The resulting fuel possesses improved thermal stability properties.

Example 3 With 100,000 parts of fuel C is blended 5 parts (0.005

percent) of 2,2-thiobis-(4-iodob-sec-dodecylphenol).

The resulting fuel blend possesses improved thermal stability characteristics. 1

Example 4 To 100,000 parts of fuel D is added 50 parts (0.05 percent) of 2,2-thiobis4( 4-chloro-G-tert-butylpherrol). The resulting fuel blend is :found to possess vastly superior thermal stability characteristics.

Example 5 With 100,000 parts of (fuel E is blended parts (0.08 percent) of 2,2 thiobis-(4-chloro-6-tert-amylphenol).

The resulting fuel blend possesses enhanced thermal stability properties.

Example 6 1 0 100,000 parts of fuel F is added 200 parts (0.2 percent) of -2,2'-thi-obis- (4 bromo=6-sec-octylphenol) dissolved in 1,500 parts of isopropanol. After mixing, the resulting fuel blend is found to possess enhanced thermal stability properties.

Example 7 To 100,000 parts of fuel H is added 150 parts (0.15 per-- cent) of 2,2'-thiobis-[4-iodo-6-(1,1,3,3tetrarnethylbutyl)- phenol]- dissolved in 1,500 parts of mixed x'ylenes. The resulting et fuel possesses superior thermal stability properties.

- Example 9 With 100,000 parts of fuel B is blended '60 parts (0.06 percent) of 2,2 thiobis- (4-chloro-6-sec-butylpl1enol). This fuel after mixing possesses improved thermal stabil ity characteristics.

- Example 10 One hundred seventy parts of 2,2'-thiobis- (4-chloro-6 isopropylphenol) is blended with 100,000 parts of fuel I. The resulting jet fuel containing 0.17 percent of the phenol possesses improved thermal stability characteristics.

TABLE I Fuel A Fuel B Fuel C Fuel Fuel E Fuel F 0 Fuel G Fuel E F (JP-3) (J P-4) (JP-5) (JP-4) (JP-4 (Kerosene (Com- (JP-5) (I l I reference) type) merclal) 10 Percent Evaporated F 154 220 395 221 380 00 Percent Evaporated: F 418 470 480 319 460 430 Endpoint F 506 550 550 480 516 -1- 519 496 524 Gravity, APT 51.8 45 35 47.3 48.5 43 42.0 43 6 41 2 Exlstent Gum, rug/ m1.,max 7 7 1.0 1.4 1.1 o 2 1'0 0'6 Potential Gum, mg./100 ml., max- 14 14 1 .0 9 .6 I field vtapor Plresrsure, pisd 5.3 3.0 0 5 0 5 roma ics v0. ercen 83 25.0 25.0 12.5 14.6 14. I

Olefins, vo'l. Percent 0 .4 a .0 s .0 0 .3 1.2 1g i Ii Ea cample 1 With 100,000 parts of fuel C is blended 70 parts (0.07 percent) of 2,2-thiolbis (4-chloro-6-tert4butylphenol). The resulting jet fuel blend possesses superior thermal stability characteristics.

Example 12 To 10,000 parts of. fuel H is added with agitation 160 parts (0.16 percent) of 2,2'-thiobis-(4-bromo-6-sec-nonylphenol) The resulting fuel is found to have greatly improved thermal stability characteristics. i

To show the great improvements in thermal stability resulting from the practice of this invention, tests were conducted in an, apparatus known as the. Coordinating Fuel Research (CPR) Jet "Fuel Coker, commonly called the Erdco Rig. "the test procedure and equipment are described in Petroleum Processing, December 1955, pages 19094911, and in Coordinating Research Council, Manual No. 3. In this equipment a jet fuel under 150 pounds presure is forced through 'a pre-heater tube having a centrally located heating element to raise the temperature of the fuel to a predetermined point. The heated fuel is then forced through a hot filter of sintered steel into a second tube. When thermal decomposition of the fuel occurs at the elevated temperature, the filter becomes plugged and a pressure drop occurs across the filter. This pressure drop is measured by a manometer placed across the filter. The following tests were conducted until a pressure drop across the fuel filter of 25" of mercury caused by decomposition of the fuel and filter plugging occurred, or if a pressure drop of 25" of mercury did not occur across the filter Within 300 minutes, the tests were discontinued. In all tests the fuel flow rate was maintained at 6 pounds per hour.

Jet fuels of thisinvention were prepared by blending 2,2-thiobis-(4-chloro-6-tert butylphenol), the most particularly preferred compound of this. invention, with samples of three different commercially available IP-S fuels which meet all of the requirements of the above mentioned military'specification except for the thermal stability properties. In these tests onJJP-S, a sample of each of the fuels without a-thermal stability additive of this invention was also tested. The testyconditions were adjusted so that the preheater temperature was 400 F. and the filter temperature was 500 F. The results of these tests are shown in Table II.

The data in 'l able II indicate that outstanding improvements in thermal stability were achieved in both of the above fuels by the addition respectively of 100 and 50 pounds per 1,000 barrels of the fuels tested. However,

in addition to the great improvement in the alleviation of filter plugging, other benefits accrue from the practice of this invention. Fuel I containing no additive, deteriorated to such an extent during the 91 minute test that the i pro-heater tube was coated with black, dark brown and tan decomposition products to the extent of 20 percent of the surfaces thereof. However, with the addition of 100 pounds per 1,000 barrels of 2,2'-thiobis-(4- chloro-6- tert-butylphenol), the deposits were reduced to a very 0 ly, in fuel K during the 39 minutes of the test on the fuel which contained no additive, :a total of 70 percent of the pre-heater surfaces were coated with deposits ranging in character from dark brown to light tan. However, with the addition of pounds per 1,000 barrels of the preferred additive of this invention, the total deposit area was reduced to 10 percent after a, 300* minute period and the deposit ranged in character from light tan to brown. In both of these instances, great improvement in the fuel was achieved by the use of the especially preferred additive oflthis invention, 2,2'-thiobis-(4-chloroo-tert-butylphenol) To further demonstrate the effects of the additives of this invention on the thermal stability properties ofjet fuels, a test was run in a commercially available JP-4 fuel. In this test the pre-heater temperature was adjusted to 300 F. and the filter was maintained at 400 F. Other test conditions were as described above. The fuel with no additive developed 25" of mercury pressure drop across the filter in 109 minutes and during this time 40 percent of the pre-heater surfaces were covered with deposits ranging from brown to tan. However, when 25 pounds per 1,000 barrels of 2,2-thiobis-(4-chloro-6-tertlbutylphenol) was added to this fuel a total pressure drop of only 7 of mercury accrued over a 300 minute period. Furthermore, the pro-heater surfaces were virtually clean under these conditions. This test further demonstrates the outstanding ability of the compounds of this invention to alleviate jet fuel thermal stability problems even at low concentrations of additive. With other compounds of this invention similar results are obtained.

. As noted about the amount of the additive of this invention used in jet aircraft fuels can range from about 0.001 to about 0.2 percent by weight. Ordinarily concentrations varying from 0.005 to about 0.05 weight percent of additive are found to be satisfactory for most present day fuels. Variations from these concentration ranges are permissible and sometimes desirable. For example, in jet fuels initially possessing a fair degree of thermal stability, very small amounts of additive are sufiicient to improve the characteristics in order to meet the military specifications, and in some cases, provide improved storage stability properties. On the other hand,

where the jet fuel initiallyhas a very poor thermal stability, larger amountsup to 0.2 percent by weight or more-can be effectively employed.

Typical jet fuel thermal stability additives of this invention include 2,2 -thiobis-(4-chloro-6-isopropylphenol), 2,2 thiobis-(4-bromo-6-sec-butylphenol), 2,2-thiobis-(4- chloro-6-tert-butylphenol), 2,2-thiobis-(4-iodo-6-sec-amylphenol), 2,2-thiobis-(4achloro-6-tert-hexylphenol) 2,2- thiobis-(4-bromo-6-tert butylphenol), 2,2-thiobis (4- iodo-o-sec-undecylphenol), and the like. As noted above the chloro compounds are preferred and the preferred alkyl group is the tertiary butyl group.

In preparing the improved fuels of this invention, the

use of solvents for the 2,2-thiobis-(4-halo-6 alkylphenol) compounds is sometimes advantageous. While the solubility of these compounds in jet fuel is sufficiently high to provide the desired concentrations blending' procedures are simplified by pre-dissolving the additives in a suitable light tan color indicating the amazing improvement in a solvent. The resulting concentrates can then be conveniently and readily blended with the jet fuels While all the components are in the liquid phase. Suitable solvents for this purpose include both aromatic and aliphatic hydrocarbons, alcohols and ketones. In general, ketones and alcohols containing up to 6 carbon atoms and liquid aromatic hydrocarbons containing 6 to 18 carbon atoms are suitable solvents. They include, for example, benzene, toluent, Xylenol, acetone, methyl ethyl ketone, methanol, diethyl ketone, ethanol, isopropanol, methyl isobutyl carbonyl and the like.

In addition to the 2,2'-thiobis-(4-halo 6 alky1phenol) thermal stabilizer of this invention, jet fuels may have agony-sulfur dichloride of sulfur mono-chloride. This preparation is illustrated by the following examples.

Example 13 A solution of 370 parts of 4-chloro-6-tert-butylphenol and 79 parts of n-hexane was stirred at 18-20 and one 7 half of a solution of 10.3 parts of sulfur dichloride and 198 parts of n-hexane was added over a 20 minute period.

' After stirring for one hour the remainder of the sulfur dichloride was added over another 20 minute period. The agitation was continued [for 2 /2 hours while the temperature was controlled at 22-25 C. During the agitation and addition of sulfur dichloride, hydrogen chloride gas was evolved. The reaction was stirred overnight and then heated for a /2 hour period at 35 C. The solvent was removed by distillation and the residue then distilled at one milliliter pressure for 100 C. The residue from this distillation was recrystallized from isooct-ane giving 19 parts of pure 2,2-thiobis-(4=chloro-6-tert-butylphenol) having a melting point of 1 -l11 Example 14 Following the general procedure of Example 13, 4- bromo-6-(24dodecyl)phenol is reacted with sulfur dichloride to produce a good yield of 2,2-thiobis-[4-bromo- 6-(2-dodecyl)phenol] One mole of the sulfur dichloride is employed for each mole of the phenol in this reaction.

Sufiicient solvent is employed to insure a mobile reaction Two moles of 4-iodo-6-isopropylphenol are reacted with one mole of sulfur dichloride at a maximum temperature of 30 C. The sulfur dichloride in n-hexane solution is added to the phenol which is also dissolved in hexane to insure maintenance of the proper temperature.

The product is recovered as described in Example 13 above .and the reaction results in a high yield of 2,2-

- thiobis-(4-iodo-6-isopropylphenol).

I claim:

1. A thermally stable jet aircraft fuel consisting essenrtially of a liquid hydrocarbon fuel heavier than gasoline having an end point of at least 435 F. and an API gravity, higher than that of hydrocarbon mineral lubrieating oil, of from 3551.8 containing from about 0.001 to about 0.2 percent by weight of a 2,2-thiobis(4-halo- 6 a1kylphenol) as a thermal stabilizing agent for said hydrocarbon fuel. v

2. The jet aircraft fuel of claim 1 wherein said liquid hydrocarbon fuel has an end point greater than 480 F.

3. A process for inhibiting the deterioration of jet aircraft fuel normally tending to occur when said fuel 8 is subjected toelevated temperatures in operation which comprises subjecting to said elevated temperatures a jet fuel consisting essentially of a liquid hydrocarbon fuel heavier than gasoline having an end point of at least 435 F. and an API gravity, higher than that of hydrocarbon mineral lubricating oil, of from 35-51.8 and from about 0.001 to about 0.2 percent by weight of a 2,2-thiobis(4-halo-6aalkylphenol) as a thermal stabilizing agent for said hydrocarbon fuel. a

4. A thermally stable jet aircraft fuel consisting essentially of liquid hydrocarbon fuel heavier than gasoline having an end point of at least 480 'F. and'an API gravity, higher than that of hydrocarbon mineral lubricating oil, of from 3551.8 containing from about 0.001

to aboutOlpercent by weight of a 2,2-thiobis(4-chloro-,

6 alkylphenol) as a thermal stabilizing agent for said hydrocarbon fuel.

5. A thermally stable jet aircraft fuel consisting essentially of liquid hydrocarbon fuel heavier than gasoline having an end point of at least 480 F. and an API gravity, higher than that of hydrocarbon mineral lubricating oil, of from 35-51.8 containing from about 0.001 to about 0.2 percent by weight of 2,2'-thiobis (4-chloro- 6-tert-butylphenol) as a thermal stabilizing agent for said hydrocarbon fuel. I

6. A process for inhibiting the deterioration of jet aircraft fuel normally tending to occur when said fuel is subjected to elevated temperature in operation which comprises subjecting to said elevated temperatures a jet fuel consisting essentially of a liquid hydrocarbonfuel heavier than gasoline having an end point of at least 480 F. and an API gravity, higher than that of hydrocarbon mineral lubricating oil, of from 3551.8 and from about 0.001 to about 0.2 percent by weight of 2,2 -thiobis (4'- I halo-6-alkylphenol). g

8. The process of claim 7 'whereinsaid thiobis phenol is 2,2'-thiobis(4-chloro-6-tentbutylphenol).'

References Cited in the file of this patent UNITED STATESIPATENTS' 2,814,597

Wenneis et al. 1... Nov. 26, 1957 2,932,942 Ecke et a1 Apr. 19, 1960 2,959,915 7 Dill'e et a l Nov. 15, 1960 FOREIGN PATENTS 201,160 Australia Jan. 11,1956

448,017 Canada Apr. 20, 1948 OTHER REFERENCES Morawetz, Phenolic Antioxidants for Paraflinic Materials, Ind. and Eng. Chem, vol. 41, No.7, July 1949 pp. 1442-1447. 

1. A THERMALLY STABLE JET AIRCRAFT FUEL CONSISTING ESSENTIALLY OF A LIQUID HYDROCARBON FUEL HEAVIER THAN GASOLINE HAVING AN END POINT OF AT LEAST 435*F. AND AN API GRAVITY, HIGHER THAN THAT OF HYDROCARBON MINERAL LUBRICATING OIL, OF FROM 35-51.8* CONTAINING FROM ABOUT 0.001 TO ABOUT 0.2 PERCENT BY WEIGHT OF A 2,2''-THIOBIS(4-HALO6-ALKYPHENOL) AS A THERMAL STABLIZING AGENT FOR SAID HYDROCARBON FUEL. 